Combination photographic etching knife and sharpener



April 22', 1941. J, G, PRATT 2,239,372

COMBINATION PHOTOGRAPHIC ETCHING KNIFE AND SHARPENER Filed Sept. 10. 1945 Patented Apr. 22, 1941 COMBINATION PHOTOGRAPHIC ETCHING KNIFE AND SHARPENER Jesse G- Pratt, Silver Spring, Md. Application September 10, 1940, Serial No. 356,224

3 Claims.

The purpose of this invention is to provide an efiicient and compact photographic etching knife and sharpening hone, the knife being easy to sharpen since the guess-work in the matter of maintaining the proper bevel has been eliminated.

Figures 1, 2, and 3 are different views of the blade holder.

Figure 4 shows a straight edge.

Figure 5 shows the end view of a blade sharpened with a double bevel.

Figure 6 shows a perspective view of honing device with knife resting thereon.

Figure 7 shows a blade sharpened with a curved edge.

Figure 8 shows the end view of a blade sharpened with a single bevel.

This device consists of a holder and knife in one unit, Figure 1; also a support I l, Figure 6, on which rests a hone, 9, Figure 6; and its adjacent slanting track l0, Figure 6.

The knife and holder unit is so constructed that when laid down on a fiat surface on either blade sharpened with a side, contact is made along the edge of a diagonal blade.

The holder is constructed by bending a strip of sheet metal to form a tube in the center 2 shown in Figures 1, 2 and 3; the two sides of the sheet metal coming together and stretching out perpendicularly from the tube I, Figure 2; these sides tapering down in width to the width of the blade 4, Figure 1, the blade being fastened at the end between the two sides of the holder.

I do not wish to restrict the construction of this instrument to metal, as it can also be constructed from Bakelite and other substances.

At the end of the tube 2, Figure 1, toward the point of the blade ll, Figure 1, is fastened an elevating device 3 protruding on each side of holder, of such height that when instrument is laid on a flat surface on either side the point of the blade will rest on such fiat surface at an appropriate cutting angle.

Tube 2 is of such size that when instrument is laid on a flat surface on either side, the heel of the blade 12 will rest on such flat surface at an appropriate cutting angle.

When elevating device 3, end of tube l3 and blade 4 are laid on a flat surface on either side, contact is made along the edge of the diagonal blade.

Moving this instrument over a flat hone will produce a straight edged blade 6, Figure 4, which is valuable for correcting drawings, etc., but is not practical for etching photographic negatives,

as films have a certain amount of curl, and such a blade would cut in at the heel or the toe.

A photographic etching knife must, therefore, have a blade with at least a slightly curved edge 5, Figure 7.

For this purpose the track In, Figure 6, is employed. The surface of the track is flat, but slants upward toward one end in relation to the flat surface of the hone 9, Figure 6.

When the blade is placed on the hone, and

the handle end of instrument rests on the lower end of the track, the heel of the diagonal blade l2, Figure 1, makes contact with the hone. As the instrument is moved forward the rising track increases the angle of bevel toward the point of the blade, so that when instrument has reached the center of the track the center of the blade is in contact; and when instrument has moved all the way to the other end of the track the entire edge of the curved blade has been brought into contact with the hone, ending up with contact at the point of the blade.

This process alternately on one side and then on the other of a curved edged blade will maintain the curved edge and keep it sharp. This process also in a short time will put a curved edge on a straight edged blade.

The track l0, Figure 6, allows greater or less curve to the blade as the amount of slant of the track is increased or decreased.

The height of the track I 0, Figure 6, in relation to the surface of the hone 9, Figure 6, when used to sharpen the instrument herein described, regulates the angle of the diagonal blade, the higher the track the more obtuse the angle, that is, the higher the track the greater the slant or tilt to the instrument when held in the hand when etching in order to bring the slightly curved edge of the blade as fiat as possible to the film. Conversely, the lower the track the less slant or tilt to the instrument when etching.

Sharpening both sides of the blade produces a double bevel I, Figure 5; doing the entire sharpening on one side of the blade produces a single bevel 8, Figure 8.

I make the following claims for my invention:

1. A blade sharpening device, comprising a support, a sharpening stone mounted on said support, and presenting a flat sharpening surface; a guiding track mounted on said support adjacent to the stone and presenting a slanting fiattop surface, one end of which is near the level of one end of the sharpening surface of the stone; a blade holder comprising an elongated member adapted to have a blade attached to one end thereof, the opposite end of said holder having a bearing portion resting upon the guide track, and constructed and arranged to position the blade holder to hold the blade in such position that the plane of the blade is tilted with respect to the surface of the sharpening stone transversely of the stone and also longitudinally of the stone.

2. A blade sharpening device, comprising a support, a sharpening stone mounted on said support, and presenting a flat sharpening surface; a guiding track mounted on said support adjacent to the stone and presenting a slanting flat-top surface, one end of which is near the level of one end of the sharpening surface of the stone; a blade holder comprising an elongated member adapted to have a blade attached to one end thereof, the opposite end of said holder having a bearing portion resting upon the guide track, said bearing portion being cylindrical and having a flange at one end thereof, so that the blade holder positions the blade so that the plane of the blade is inclined with respect to the surface of the sharpening stone transversely of said surface and also longitudinally of said surface.

3. A blade sharpening device, comprising a support, a sharpening stone mounted on said support, and presenting a fiat sharpening surface; a guiding track mounted on said support adjacent to the stone and presenting a surface which slants with respect tov the sharpening surface longitudinally thereof; one end of which is near the level of one end of the sharpening surface of the stone; a blade holder comprising an elongated member adapted to have a blade attached to one end thereof, the opposite end of said holder having a bearing portion resting upon the guide track, said bearing portion having a flange at one end thereof so that the blade holder positions the plane of the blade so that it is inclined with respect to the surface of the sharpening stone transversely of said surface and also longitudinally of said surface.

JESSE G. PRATT. 

